Device and method for carrying out a two-stage linear movement

ABSTRACT

A device for carrying out a two-stage, linear movement as well as an associated method for displacing a displaceable structural unit relative to a stationary structural unit. A first drive unit drives a shaft, which is in operative connection with a tube, which is connected to the displaceable structural unit. If a predeterminable condition is substantially achieved, a switch is made from the first drive unit to a second drive unit. Because the tube extends through the stationary structural unit and is displaced relative to the stationary structural unit when the first drive unit is actuated, the at least one separating means being jointly displaceable with the second drive unit and coupling in a detachable manner the tube to the second drive unit initially when the condition is achieved and thereby separating the shaft from the flow of force, as soon as the second drive unit is actuated alone, the members, which transfer the rotary movement into a straight movement, can be protected in a two-stage linear movement.

FIELD OF THE INVENTION

The invention relates to a device for carrying out a substantiallytwo-stage linear movement, which is usable preferably, but not only, ona plastics injection molding machine.

STATE OF THE ART

A device of this type is known from DE 195 42 453 C2. A shaft with ahead with external thread lies in a tube with internal thread. Cylinderor rolling bodies in the form of planets are preferably disposed betweenshaft and tube, are mounted so as to be non displaceable axiallyrelative to the head and are in operative connection with the twothreads of head and tube. Another tube is disposed around the shaft soas to be nor-displaceable relative to this latter and, when theelectromechanical unit is displaced, moves into the tube, which isprovided with the internal thread, and moves out of the same. The shaftis mounted via cup springs in such a manner that when the shaft isactuated via a first drive unit, it can move just until a greater forceis applied, e.g. via a second drive unit. Consequently, the shaft can,where applicable, be separated from the flow of force and the forces aretransmitted via the two interlocking tubes, a gradual transfer from theone drive unit to the other is not possible.

Japanese Patent Application JP-A 9-29802 shows a two-stage closingmechanism, where the traveling motion is initially effected via athreaded shaft with a small diameter, whilst the applying of the closingforce is then effected via a threaded shaft with a large diameter. Thesmall shaft, to this end, engages via a thread in the large shaft in acoaxial manner. During the traveling motion a nut, which is in operativeconnection with the external thread of the threaded shaft with thelarger diameter, is entrained in a passive manner. When the closingforce is to be applied, a sleeve is impinged upon hydraulically, wherebya gap between nut and sleeve is initially closed. With further movement,the nut is pressed by the sleeve into a position, in which the closingforce can be applied and the shaft is blocked. Through the thread,however, the point of contact alters depending on the position in such amanner that the result is variable from injection cycle to injectioncycle.

Japanese Patent Application JP-A 4-332616, for the traveling motion whenthe molds are run together, has a ball roller spindle, which plungesinto the piston rod of a closing cylinder with the mold in the openedstate. For actuating the piston rod of the closing cylinder, there is aball roller nut disposed at its end, which ball roller nut interactswith the ball roller spindle. To relieve the ball roller spindle, whichis not designed for the closing forces, and to apply the closing force,there is an adjusting mechanism provided which is designed so as to bespline-like. On the mold-side end of the closing cylinder and on the endof the closing piston remote from the mold, there are projectionsprovided which slide past one another during the mold closing movement,but which on the other hand are also for transferring the mold forcesfrom the closing cylinder to the closing piston. Consequently, viacorresponding auxiliary means, the parts of this locking mechanism arerotated in such a manner that the closing force can then be applied bydosing the gap d. This is also dependent on the position and varies fromcycle to cycle.

DE 195 36 565 A1 makes known an electromechanical drive, where also theparts of a threaded rolling planetary spindle are secured via securingmeans, such as, for example, springs, against passive reversing. Thereis a two-stage movement, however the rolling bodies are continuously inthe flow of force. The second drive unit is not actuated until the firstdrive unit is secured.

The series closing of the mold of an injection molding machine is known,for example, in EP 0 674 985 A1, where forces are directed both when thedisplaceable mold carrier is moving to form closure and when the holdingforce is applied constantly via spindles, which are to be dimensionedaccordingly.

WO 92/11993 A1 makes known providing a hydraulic piston cylinder unitwith a plunger piston, which at the same time is in operative connectionwith a threaded spindle. There are no means provided for the effectiveseparating of the threaded spindle from the flow of force.

SUMMARY OF THE INVENTION

Proceeding from the state of the art, it is the object of the presentinvention, in the case of a substantially two-stage linear motionalaction, to protect the members, which transmit the rotary movement forachieving the straight movement.

This object is achieved through a device for carrying out asubstantially two-stage linear movement comprising: a stationarystructural unit; a displaceable structural unit; at least one firstelectromechanical drive unit mounted on the stationary structural unit;at least one shaft rotatably driven by the first drive unit and having aregion with an external thread; at least one tube with an internalthread, which tube is disposed coaxially relative to the respectiveshaft, is displaced with the displaceable structural unit and is inoperative connection with the external thread for the displacement ofthe displaceable structural unit; separating means for a separation ofthe shaft at least from a further flow of force when at least onepredeterminable condition is obtained, the predeterminable conditionincludes a translatory position of the tube and a predeterminable axialforce; and at least one second drive unit, which is actuatable once thepredeterminable condition has been achieved, wherein the tube extendsthrough the stationary structural unit and is displaced relative to thestationary structural unit when the first drive unit is actuated, theseparating means being jointly displaceable with the second drive unitand, when the predeterminable condition is achieved, the tube is firstlycoupled in a detachable manner to the second drive unit and in so doingseparates the shaft at least from the further flow of force, which isproduced by the second drive unit, as soon as the second drive unit isactuated alone, and that the separating means works radially on thetube.

This object is also achieved through a method for performing asubstantially two-stage, linear movement, the method comprising:actuating a shaft by means of at least a first electromechanical driveunit until a predeterminable condition is obtained, the firstelectromechanical drive unit is mounted on a stationary structural unit;separating the shaft at least from the further flow of force, when thepredeterminable condition is achieved, by separating means that workradially on the tube; actuating at least a second drive unit once thepredeterminable condition has been achieved, for the displacement of thedisplaceable structural unit via the tube, which is disposed coaxiallyrelative to the respective shaft, which is displaced with thedisplaceable structural unit and is in operative connection with theshaft; and displacing the tube relative to the stationary structuralunit when the first drive unit is actuated, the separating means beingjointly displaceable with the second drive unit and, when thepredeterminable condition is achieved, the tube is firstly coupled in adetachable manner to the second drive unit and in doing so separates theshaft at least from the further flow of force produced by the seconddrive unit, as soon as the second drive unit is actuated alone.

The tube, which has the internal thread, is preferably disposed in sucha manner that, on account of the actuation of the first drive unit, thetube is not only displaced relative to the stationary structural unitbut also extends through this unit. At the same time, separating means,which are displaceable jointly with the second drive unit, are disposedin such a manner for the separation, where applicable, of the shaft ofthis first drive unit from the flow of force that, for example, a freemovement is possible during the actuation of the first drive unit.However, as soon as, preferably, a predetermined limiting conditionoccurs, the first drive unit, with the exception of the tubetransmitting the forces, can be released. Consequently, the parts of theelectromechanical drive unit, which are in operative connection with oneanother via the threads (head of the shaft, rolling bodies), oralternatively a linear motor forming the first drive unit, are notexposed to the forces from the second drive unit and can accordingly bedimensioned for the transfer of smaller forces. Costly self-lockingthreads on the electromechanical drive unit are not necessary.

SHORT DESCRIPTION OF THE FIGURES

The invention is explained below by way of the exemplified embodimentsrepresented in the Figures. In which:

FIG. 1 is a front view of a closing unit situated on a machine base,

FIG. 2 is an enlarged, partially sectioned cut-out from FIG. 1 in theregion of the stationary structural unit with opened tool,

FIG. 3, 4 are enlarged cut-outs from FIG. 2 in the region of thestationary structural unit in two exemplified embodiments of hydraulicseparating means,

FIG. 5 is a representation as in FIG. 2 with a magnetically actuatablesecond drive unit,

FIG. 6 is a representation as in FIG. 5 with a linear motor as firstdrive unit.

DETAILED DESCRIPTION

The invention is now described in more detail as an example withreference to the enclosed drawings. The exemplified embodiments are,however, only examples, which are not to restrict the inventive conceptto any specific arrangement.

The Figures show a device for carrying out a substantially two-stage,linear movement on a plastics material injection molding machine, whichis suitable for processing plastics materials and other plasticizablesubstances such as powdery substances or ceramic substances. Althoughthe device is explained below on this injection molding machine, it cancertainly be used in general for a two-stage linear movement of machineparts, such as, for example, with machine tools and robots. If it isimportant for some machines to carry out movements rapidly, strongforces are more important to other machines. In the case of plasticinjection molding machines, for example, the requirements for theclosing unit in FIG. 1 change during the displacement procedure. Thus,when the mold 31 is closed, the displaceable mold carrier, asdisplaceable structural unit 11, is to be closed as rapidly as possibleinitially at a predetermined speed profile using little force, whilstduring the further closing movement, a strong holding force isnecessary.

FIG. 1 shows the design of a mold closing unit, which is disposed on amachine base 33. The mold closing unit has a supporting member asstationary structural unit 10 and a stationary mold carrier 30.Stationary mold carrier 30 and stationary structural unit 10 areinterconnected via braces or tie bars, which act as guiding means on onehand of the displaceable structural unit 11 (displaceable mold carrier)and at the same time are configured as force transmitting members fortransmitting the forces occurring during the injection molding process.

The closing movement or respectively the actual supplying of the mold iseffected via a first electromechanical drive unit 12, which is mountedon the stationary structural unit 10. The further movement orrespectively the applying of the holding force is effected through theuse of a second hydraulic drive unit 17 as in FIGS. 2 and 3.

As shown in FIGS. 2 and 3, the electromechanical drive unit 12 has arotatably driven shaft 13, which is mounted on the drive unit 12 via abearing arrangement 27. The shaft 13, in its turn, has a region withexternal thread 14 a, in the exemplified embodiment the head 14. Theshaft 13, itself, is displaced in a rotary manner and is fixed so as tobe substantially non-displaceable axially when the first drive unit isactuated in the direction of the shaft. The only axial movement isallowed through the cup springs 28, which are to be explainedsubsequently.

An internal thread 15 a of a tube 15 is in operative connection with theexternal thread 14 a of the head 14. This tube 15 is displaced jointlywith the displaceable structural unit 11 and is disposed coaxiallyrelative to the shaft 13. Although this is not necessary in principle,for simplifying the rotary movement, cylinder or rolling bodies 16,which are retained opposite the shaft 13 between the shaft 13 and thetube 15 so as to be non displaceable in the axial direction of theshaft, are disposed in the form of planets. If the shaft 13 is rotated,the head 14 with its external thread 14 a sets the planets in rotationsuch that there is an axial movement of the tube 15 on account of theengagement of these planets in the internal thread 15 a of the tube 15.According to FIGS. 2 and 3, the tube 15 is disposed in such a mannerthat it extends through the stationary structural unit 10 and, onaccount of the actuation of the first drive unit 12, is displacedrelative to this stationary structural unit 10. The drive units arepreferably disposed in such a manner that the electromechanical driveunit 12 is situated at a fixed spacing from the stationary structuralunit 10, whilst the second drive unit 17 is disposed on the stationarystructural unit. The successful friction-locking of the tube 15 makes itpossible in a simple manner for the annular piston 18 of the seconddrive unit 17 to be able to work directly on the tube 15 for thetransferring of further forces.

If a predeterminable condition is achieved, which, for example, can be aspecific translatory position of the tube 15 (e.g. a position just infront of a mold closure in the case of a plastic injection moldingmachine in order to carry out a subsequent injection embossing process)or the achieving of a predeterminable axial force, the shaft 13 isdisengaged through separating means 23, 23′, 38, where applicable, atleast from the further flow of force, but also, where applicable, fromall flow of force. The further application of force and/or movement iseffected substantially via a second drive unit 17 once thispredetermined condition has been achieved. This predetermined condition,however, can include a plurality of individual conditions if, forexample, the two drive units are actuated jointly over a certain periodwhat is explained below.

The separating means 23, 23′, 38 for the separating of the shaft, whereapplicable, are disposed on the stationary structural unit 10 so as tobe jointly displaceable with the second drive unit 17. When thepredeterminable condition has be en achieved, these fix the tube 15directly or indirectly to the stationary structural unit 10 in adetachable manner. At the same time, the separating means 23, 23′, 38connect the tube initially for joint displacement in a detachable mannerto the second drive unit 17. At the same time, this prepares theseparation of the shaft 13 from at least the further flow of force. Assoon as namely the second drive unit 17 is actuated alone, the shaft 13is released. A complete separation is not necessary here. It suffices ifthe further forces, which are applied by the second drive unit 17,remain substantially without further influence on those members which upto now have been in the flow of force of the first drive unit, thesemembers, however, still continuing to be under the influence of theprevious forces. In this case, there is a force superposition with noeffect on these members. As can be seen in FIGS. 1 and 2, the firstdrive unit 12 is mounted via connecting means 29 on the side of thestationary structural unit 10, which is remote from the displaceablestructural unit 11. This means that, in principle, the position of thehead 14 no longer alters relative to the stationary structural unit. Theshaft 13 is surrounded by another tube 34 such that with the axialmovement of the tube 15 and also on account of the closing member 35,the compressing of a piston cylinder unit is produced externally, the“piston” withdrawing from the “cylinder”. Permanent lubrication for thefirst drive unit can be applied in the interior in this way.

The separating means 23, 23′, 38 lock the tube 15 in a friction-lockingmanner and where only one tube is used in a central manner, as soon as,in the case of the injection molding machine, for example, the moldclosure has been achieved and a corresponding signal is given in orderto act upon the hydraulic separating means 23, 23′, 38, in theexemplified embodiment, by bringing hydraulic media into the cylinderareas 36, 37. This means that the separating means, where applicable,are actively actuatable at any time, without a certain external forcehaving first to be active. In this respect, for example, in the case ofinjection embossing using a plastics injection molding machine, a changecan be made at an arbitrary moment from one drive unit to the otherindependent of the respective forces.

As can be seen in FIG. 2, the second drive unit 17 has as piston anannular piston 18, which surrounds the tube 15 in a coaxial manner. Thecylinder for this piston 18 is formed by a recess 19 in the stationarystructural unit 10. The cylinder areas 20, 21 are defined in the axialdirection of the tube 15 by the base 19 a of the recess 19 as well as byan annular flange 22. The separating means 23, 23′, 38 are disposed onthe displaceable portion of the second drive unit, for example, on theannular piston 18 or on an intermediate element 39 independently in sucha manner that once the separating means 23, 23′, 38 have been actuated,an impingement of the annular piston 18 or a displacement of theintermediate element 39 results in the tube 15 also being displacedaxially with annular piston or intermediate element. In the closingprocess, pressure is applied to the cylinder area 20, in the openingprocess pressure can be applied to the cylinder area 21, but this is noturgently necessary as purely through the abating of the pressure in thecylinder area 20, a return movement is set up such that, after releasingthe locking through the separating means 23, 23′ 38, the continuedmovement can be effected through the first drive unit 12, in the case ofan injection molding machine as opening movement of mold 31.

The arrangement of the separating means on the second drive unitconsequently also makes it possible to actuate the firstelectromechanical drive unit 12 and the hydraulic second drive unit 17simultaneously at least part time to achieve a superposing movement. Inthis way, for a example, on an injection molding machine during theinjection embossing process, that is injecting into the mold gap, whichis still open, before the final mold closure, the first drive unit 12can still be actuated, whilst the second drive unit is already inoperation. It is especially advantageous, however, that this makes itpossible to transfer the load for a transition period gradually from thefirst drive unit to the other and vice versa. In this respect only asubstantially two-stage linear movement exists, as between the twostages both drive units are actuated during a period of transition.Through the superposing of the two movements, which consequentlyfollows, a seamless, jerk-free transition can be effected easier thanbefore. In this position, however, the one predeterminable conditionbecomes at least two predeterminable conditions. As soon as namely onecondition is achieved, the separating means 23, 23′, 38 are actuated.The second drive unit 17 is then connected, however with the first driveunit 12 not yet being disconnected until a further condition isachieved. However, the continued movement is taken over substantially bythe second drive unit 17 in such a manner that it can be said that onepredetermined condition is substantially achieved.

FIG. 4 shows a first embodiment of the separating means 23 in the formof a hydraulic tension clamp. In this embodiment, the annular piston 18has a flange 18 a, which extends along the tube 15. This flange canitself have a cone. In the embodiment, a collet 24 with cone is mountedon this flange 18 a. To form the tension clamp, this cone interacts witha counter cone of another annular piston 25, which in its turn ismounted on the first annular piston 22. If, in the case of thisexemplified embodiment, the predeterminable condition for switchingbetween the first drive unit and another drive unit or for connectingthe second drive unit 17 is achieved, by applying a pressure to thecylinder area 36, the other annular piston 25 in FIG. 4 is initiallymoved to the right. This tensions the two cones of the other annularpiston 25 and the collet 24 together such that the tube 15 isfrictionally tensioned. The annular piston 18 can then be moved jointlywith the tube 15 through pressure build-up in the cylinder area 20 ofthe second drive unit 17.

As an alternative, FIG. 3 shows a hydraulic clamping sleeve 26 asseparating means 23′. In this case, pressure is applied to the cylinderarea 37 as soon as the predeterminable condition is achieved and thisresults in frictional tensioning between tube 15 and annular piston 18.

As can be seen in FIG. 2, the shaft 13 is supported in a resilientmanner via cup springs 28 on the first drive unit 12. Without this typeof resilient cushioning, there would be a danger that when the seconddrive unit is actuated and the flow of force is from the tube via theseparating means 23, 23′, 38 and the annular piston 18 to the stationarystructural unit, there would be a relative movement between stationarystructural unit and tube, which would stress the rolling or cylinderbodies 16 and the shaft 13. To avoid this and to protect the rolling orcylinder bodies as much as possible, the cup springs 28 are provided inthe region of the bearing arrangement 27. The cup springs 28 can alsowork as damping members in the case of the abovementioned superposedmovement, as the torque of the first drive unit 12 can be restricted. Ifthere are no cup springs 28, the drive unit 12 can also have a torquerestricting means as an alternative.

To ensure that when the tube 15 and the annular piston 18 are tensioned,as little force as possible is transferred to the rolling and cylinderbodies 16 and the head 14, the first drive unit 12 is supported on thestationary structural unit 10 via the connecting means 29 in such amanner that the head 14 of the shaft 13, which head 14 has the externalthread 14 a, comes to lie in the opening 10 a of the stationarystructural unit 19, but is axially spaced from the separating means 23,23′ in the axial direction of the tube. The arrangement of the head 14inside the opening 10 a of the stationary structural unit isadvantageous as, as can be seen when comparing FIG. 2 and FIG. 3, thetube 15 can be displaced to the right in FIG. 2 when the first driveunit is actuated until, as in FIG. 3, the stop member 35 a of the cover35 abuts the stationary structural unit.

The design of the device for carrying out a two-stage, linear movementhas been explained up to now by way of one tube with one shaft and oneelectromechanical drive unit. In principle, it is possible to arrange aplurality of these devices in parallel. The advantage of the solutionwith only one tube and one drive unit is that a central clampingprocedure is possible without there being any danger that, with aplurality of clamping procedures being effected parallel to one another,the individual devices are no longer parallel. When using only a simpleclamping procedure, there are no more synchronization problems.Nevertheless, a plurality of these devices is also usable one next tothe other.

FIGS. 5 and 6 show other embodiments, where the second drive unit 17 isactuatable in a magnetic manner. When actuated once the condition isachieved, the separating means 38 fix the tube 15 to an intermediatemember 39, which is disposed on the stationary structural unit 10. Theintermediate member 39, which is configured as a support plate, canitself be magnetic or magnetically actuatable or can have a magneticplate 40, as in FIG. 5. The stationary structural unit can also beprovided with a magnetic plate 41. Consequently, the intermediate member39 can be moved jointly with the tube 15 at least through theintermediary of the magnetic attractive forces produced by the seconddrive unit 17 for the application of the closing force in the directionof closure s-s. The movement is effected within a cover 42.

The magnetic plates 40, 41 correspond to one another such that the areaavailable in conjunction with the spacing between the magnetic plateswhen connecting the second drive unit determines the magnetic forcesavailable. Consequently, the intermediate member 39 in its dimensions inthe horizontal projection in the direction of closure s-s is preferablyapproximately as large as the stationary structural unit 10. With thistype of design, it is possible to apply the closing force magneticallythrough the second drive unit 17. As the magnetic force increasesexponentially as the spacing between the magnetic plates decreases, iteasily generates a high closure force. For opening and, whereapplicable, pulling apart the mold, only the polarity has to be changedso that the first drive unit is not loaded with additional forces.

As can be seen in FIGS. 5 and 6, the connecting means 29 act as guidingmeans to the intermediate member 39 via friction bearing 44. Themovement of the intermediate member is defined by stop members 45. Ascan be seen in FIG. 6, the first drive unit 12 can also be anelectromagnetically operated linear motor 47, a portion of which isformed by the linear displacing means 15, whilst the enclosed stator, asin the case of the electromechanical drive unit, is supported by theconnecting members 29 on the stationary structural unit 10. The at leastone separating means 38 locks the linear displacing means 15 in africtional manner, for example in a hydraulic manner. The separatingmeans 38 can also be actuated through the intermediary of a linearmotor.

As can be seen in FIGS. 5 and 6, the separating means 38 work as atension clamp. An annular piston 25, for example, can be movedhydraulically or magnetically in closing direction s-s in a housing 43,which is disposed coaxially relative to the tube 34. An annular sleeve46 with cone is connected to the annular piston. This cone interactswith a counter cone on the intermediate member 39 to form the tensionclamp. If the predeterminable condition is achieved in the case of thisembodiment, the annular piston 25 as in FIGS. 5 and 6 is initiallydisplaced to the left. This makes the two cones of the annular piston 25and of the intermediate member 39 tension together such that the tube 15is frictionally tensioned. The intermediate member 39 can then be movedjointly with the tube 15 through the magnetic forces of the second driveunit 17.

The device operates, for example, as follows. Initially the drivingmember of at least a first drive unit 12, which is mounted on thestationary structural unit 10, is actuated until the predeterminablecondition is achieved. The driving member is then separated from theflow of force through the intermediary of the separating means 23, 23′,38, when achieving the predeterminable condition, as far as necessary.The further movement is effected at least substantially throughactuation of at least a second drive unit 17 substantially afterachieving the predeterminable condition for the displacement of thedisplaceable structural unit 11. To this end at least one tube 15, whichis displaced with the displaceable structural unit 11, is in operativeconnection with the shaft 13. When the first drive unit 12 is displaced,the tube 15 is displaced relative to the stationary structural unit 10.It actually slides through the stationary structural unit 10. When thecondition is achieved, the separating means 23, 23′, 38, disposed on thestationary structural unit 10, locks or clamps the tube 15 in adetachable and preferably frictional manner. The separating means 23,23′ can be actively connected through impingement of the associatedcylinder areas 36, 37 or can be actively connected in a magnetic manner.To achieve a superposing movement, the first drive unit 12 and thesecond drive unit 17 can be actuated simultaneously at least part-time.

This description can be subject to the most varied modifications,alterations and adaptations, which range in the region of equivalents tothe attached sub claims. Moreover, the present application claimspriority to German patent application 199 56 190.7, filed on Nov. 22,1999, the content of that disclosure of which is herein incorporated byreference in its entirety.

What is claimed is:
 1. Device for carrying out a substantially two-stagelinear movement comprising: a stationary structural unit; a displaceablestructural unit; at least one first electromechanical drive unit mountedon the stationary structural unit; at least one shaft rotatably drivenby the first drive unit and having a region with external thread; atleast one tube with internal thread, which tube is disposed coaxiallyrelative to the respective shaft, is displaced with the displaceablestructural unit and is in operative connection with the external threadfor the displacement of the displaceable structural unit; separatingmeans for a separation of the shaft at least from a further flow offorce when at least one predeterminable condition is obtained, thepredeterminable condition includes at least one of a translatoryposition of the tube and a predeterminable axial force; at least onesecond drive unit, which is actuatable once the predeterminablecondition has been achieved, wherein the tube extends through thestationary structural unit and is displaced relative to the stationarystructural unit when the first drive unit is actuated, the separatingmeans being jointly displaceable with the second drive unit and, whenthe predeterminable condition is achieved, the tube is firstly coupledin a detachable manner to the second drive unit and in so doingseparates the shaft at least from the further flow of force, which isproduced by the second drive unit, as soon as the second drive unit isactuated alone, and that the separating means works radially on thetube.
 2. Device according to claim 1, wherein the separating means isactively actuatable through impingement of associated cylinder areas. 3.Device according to claim 1, wherein the separating means is activelyactuatable in a magnetic manner.
 4. Device according to claim 1, whereinthe separating means friction-lock the tube in a central manner once thepredetermined condition has been obtained.
 5. Device according to claim1, wherein the second hydraulic drive unit has as piston a rotary pistonthat surrounds the tube coaxially and a cylinder of which is formedthrough a recess in the stationary structural unit.
 6. Device accordingto claim 5, wherein the cylinder areas of the second drive unit aredefined in a direction of the rotary piston by a base of the recess andby an annular flange, which is mounted on the stationary structuralunit.
 7. Device according to claim 1, wherein to obtain a superposeddisplacement, the first drive unit and the second drive unit areactuatable simultaneously at least at times.
 8. Device according toclaim 1, wherein the separating means is configured as a hydraulicallyor magnetically actuatable tension clamp.
 9. Device according to claim1, wherein the separating means is configured as a hydraulically ormagnetically actuatable tension clamp, wherein the second hydraulicdrive unit has a first rotary piston, and wherein the tension clamp isformed by a collet having a first cone that interacts with a second coneof a second rotary piston, the second rotary piston is mounted in thefirst rotary piston, the collet is mounted on a flange of the secondrotary piston and the flange extends along the tube.
 10. Deviceaccording to claim 1, wherein the separating means is formed by ahydraulic clamping sleeve.
 11. Device according to claim 1, wherein amounting of the shaft is supported on the first drive unit in aresilient manner via cup springs.
 12. Device according to claim 1,wherein the first drive unit is supported on a side of the stationarystructural unit remote from the displaceable structural unit.
 13. Deviceaccording to claim 1, wherein the first drive unit is supported on thestationary structural unit via connecting means in such a manner that ahead of the shaft, which bears the external thread, is disposedapproximately in an opening of the stationary structural unit. 14.Device according to claim 13, wherein the separating means, which workradially on the tube, is at a spacing from the head in the axialdirection of the tube.
 15. Device according to claim 1, wherein thestationary structural unit is a supporting member of a substantiallytwo-stage, linear closing unit on a plastics injection molding machineand the displaceable structural unit is the displaceable mold carrier ofa plastics injection molding machine.
 16. Device according to claim 1,wherein the first drive unit is a portion of a magnetically operatedlinear motor being in operative connection with the tube.
 17. Deviceaccording to claim 1, wherein the separating means, when actuated oncethe predeterminable condition has been obtained, secure the tube to anintermediate member and in that the intermediate member is displaceablein a closing direction at least by means or magnetic attractive forcesproduced by the second drive unit to provide a closing force in theclosing direction (s-s).
 18. Method for performing a substantiallytwo-stage, linear movement, the method comprising: actuating a shaft bymeans of at least of a first electromechanical drive unit until apredeterminable condition is obtained, the first electromechanical driveunit is mounted on a stationary structural unit; separating the shaft atleast from the further flow of force, when the predeterminable conditionis achieved, by separating means that work radially on the tube;actuating at least a second drive unit once the predeterminablecondition has been achieved, for a displacement of the displaceablestructural unit via at the tube, which is disposed coaxially relative tothe respective shaft, which is displaced with the displaceablestructural unit and is in operative connection with the shaft; anddisplacing the tube relative to the stationary structural unit when thefirst drive unit is actuated, the separating means being jointlydisplaceable with the second drive unit, and when the predeterminablecondition is achieved, the tube is firstly coupled in a detachablemanner to the second drive unit and in doing so separates the shaft atleast from the further flow of force produced by the second drive unit,as soon as the second drive unit is actuated alone.
 19. Method accordingto claim 18, wherein the separating means is actively connected throughimpingement of associated cylinder areas or respectively is activelyconnected in a magnetic manner.
 20. Method according to claim 18,wherein the separating means friction-lock the tube in a central manneronce the predeterminable condition is achieved.
 21. Method according toclaim 18, wherein to obtain a superposed displacement, the first driveunit and the second drive unit are actuated simultaneously at least attimes.
 22. Device according to claim 1, further comprising rollingbodies disposed between the shaft and the tube and retained so as to benon-displaceable in an axial manner opposite the shaft.
 23. Device forcarrying out a substantially two-stage linear movement comprising: astationary structural unit; a displaceable structural unit; at least oneshaft having a region with external thread; at least one first driveunit mounted on the stationary structural unit, the first drive unitproduces a force on the shaft so that the shaft is rotatably driven bythe first drive unit; at least one tube with internal thread, which tubeis disposed coaxially relative to the shaft, is displaced with thedisplaceable structural unit and is in operative connection with theexternal thread for the displacement of the displaceable structuralunit; separating means for a separation of the shaft at least from afurther flow of force when at least one predeterminable condition isobtained, the predeterminable condition includes at least one of atranslatory position of the tube and a predeterminable axial force; atleast one second drive unit, which is actuatable once thepredeterminable condition has been achieved, wherein the tube extendsthrough the stationary structural unit and is displaced relative to thestationary structural unit when the first drive unit is actuated, theseparating means being jointly displaceable with the second drive unitand, when the predeterminable condition is achieved, the tube is firstlycoupled in a detachable manner to the second drive unit and in so doingseparates the shaft at least from the further flow of force, which isproduced by the second drive unit, as soon as the second drive unit isactuated alone, and that the separating means works radially on thetube.
 24. Device for carrying out a substantially two-stage linearmovement comprising: a stationary structural unit; a displaceablestructural unit; at least one first electromechanical drive unit mountedon the stationary structural unit; at least one shaft rotatably drivenby the first drive unit and having a region with external thread; atleast one tube with internal thread, which tube is disposed coaxiallyrelative to the respective shaft, is displaced with the displaceablestructural unit and is in operative connection with the external threadfor the displacement of the displaceable structural unit; separatingmeans for a separation of the shaft at least from a further flow offorce when at least one predeterminable condition is obtained, thepredeterminable condition includes at least one of a translatoryposition of the tube and a predeterminable axial force; at least onesecond drive unit, which is actuatable once the predeterminablecondition has been achieved, wherein the tube extends through thestationary structural unit and is displaced relative to the stationarystructural unit when the first drive unit is actuated, the separatingmeans being jointly displaceable with the second drive unit and, whenthe predeterminable condition is achieved, the tube is firstly coupledin a detachable manner to the second drive unit and in so doingseparates the shaft at least from the further flow of force, which isproduced by the second drive unit, as soon as the second drive unit isactuated alone, and that the separating means works radially on thetube, and wherein the separating means is configured as a hydraulicallyor magnetically actuatable tension clamp and wherein the separatingmeans is formed by a hydraulic clamping sleeve.